1. Field of the Invention
This invention relates to a carrying truck for carrying a work such as a body of an automobile in a factory.
2. Description of the Related Art
Conventionally, various carriers for carrying a work between various working steps such as a carrying truck and a skid carrier are used in a factory.
FIG. 8 shows an example of a carrying truck for receiving a work W such as a body of an automobile and carrying the work in an oven in order to dry the work W after the work W is painted in a painting step. Referring to FIG. 8, a carrying truck A1 has four flanged traveling wheels A2 on a lower face of a body thereof. The traveling wheels A2 are supported on a pair of rails A4 secured to a support frame A3 on a floor face G in the oven and hauled by a truck carrying conveyor A5 provided between the rails A4 to carry the work W.
The truck carrying conveyor A5 has a trolley A8 guided and supported for traveling movement by and on guide rollers A7 which are rolled on a pair of guide rails A6 having a channel-shaped cross section and disposed in an opposing relationship to each other on the opposite left and right sides of the trolley A8. The trolley A8 of the truck carrying conveyor A5 is connected to a conveyor chain not shown such that, when the conveyor chain is driven, the carrying truck A1 travels.
Meanwhile, FIG. 9 shows an example of a skid carrier for receiving a work W and carrying it in an oven. Referring to FIG. 9, the skid carrier is generally denoted at B1. A skid carrying roller conveyor B2 includes a support frame B3 located on a floor face, and a large number of flanged free rollers B4 arranged along a carrying direction at one of the opposite ends of the support frame B3 in a widthwise direction. A large number of drive rollers B5 are disposed at the other end portion of the support frame B3 in the widthwise direction in an opposing relationship to each of the flanged free rollers B4.
Each of the flanged free rollers B4 is mounted for free rotation around a horizontal axis and has a pair of flanges F formed on the opposite sides of an outer periphery thereof. Each of the flanged free rollers B4 thus guides, with the flanges F thereof, the opposite side faces of a roller contacting portion t provided at a bottom portion of one of a pair of skid legs B6 of the skid carrier B1, on which a work W is received, and receives, at the outer periphery thereof, the lower face of the roller contacting portion t.
Each of the drive rollers B5 receives, at an outer periphery thereof, the lower face of the roller contacting portion t of the other skid leg B6 of the skid carrier B1 so that the skid carrier B1 is carried by rotation of the drive roller B5.
In the conventional carrying truck A1 described above with reference to FIG. 8, since the traveling wheels A2 at the lower portions of the body are rolled on the rails A4 to cause the carrying truck A1 to travel, where the carrying truck A1 changes a truck carrying conveyor from a current step to a next step, where the carrying truck A1 transfers between a truck carrying conveyor and a traverser for carrying to an orthogonal carrying line or where the carrying truck A1 transfers between a truck carrying conveyor and a lifter, the allowable track connection distance or the allowable track offset distance between the rails A4 provided on the truck carrying conveyor, traverser, lifter and so forth are approximately 10 mm in the maximum particularly where such a work W as a body of an automobile is carried. If this allowable distance is exceeded, then smooth transfer becomes difficult, and high transferring power is required and accidental dislocation of the traveling wheels from the rails may possibly occur. Therefore, a carrying line must be designed taking prevention of such accidental dislocation as described above sufficiently into consideration.
Accordingly, where a carrying line for such a conventional carrying truck A1 as described above is laid, there is a problem that a heavy construction burden and a high cost are imposed in order to secure an appropriate allowable track connection distance and an appropriate allowable offset distance of the rails A4 which is heavy, thick, long and large.
Further, the conventional carrying truck A1 described above cannot be applied to a carrying line which includes such a skid carrying roller conveyor B2 as a roller conveyor or a friction roller conveyor because it does not have a lower body frame elongated in a carrying direction as is intended so as to engage with and be carried by the skid carrying roller conveyor B2 such as a roller conveyor or a friction conveyor. Therefore, there is a difficult problem that, in order to perform working operation for a work W, which has been carried by the carrying truck A1, on a carrying line which includes such a skid carrying roller conveyor B2 as described above, the work W must be transferred from the carrying truck A1 to the skid carrier B1.
Meanwhile, in the conventional skid carrier B1 described above with reference to FIG. 9, since it does not include wheels for traveling and the overall weight of the skid carrier B1 on which the work W is loaded is received by the large number of flanged free rollers B4 disposed on the skid carrying roller conveyor B2 side, a sufficient strength which eliminates distortion or deflection of the skid carrier B1 in its longitudinal direction must be assured. Consequently, the conventional skid carrier B1 has a problem in designing that the weight of the skid carrier B1 cannot be reduced readily.
Further, since the skid carrier B1 described above does not include such traveling wheels A2 as described above, even if a traverser is used, the skid carrier B1 cannot be removed from an ordinary carrying line to an arbitrary refuge area, different from the conventional carrying truck A1 which includes the traveling wheels A2, but the position for removal is limited only to a specific refuge area in which a large number of free rollers are provided on the floor. Therefore, the skid carrier B1 cannot take refuge to an arbitrary position. Where a large number of free rollers are provided specifically on the floor over a wide refuge area, this increases the cost for the equipment significantly and besides gives rise to restrictions to safety in working such as the necessity to draw a worker's attention so that the worker may not inadvertently step on the free rollers. Accordingly, there is a problem in working schedule control that it cannot be anticipated to maintain a predetermined production processing efficiency when a countermeasure against a trouble on the carrying line is taken.
Further, when it is tried to transfer such a skid carrier B1 as described above to a turntable or the like to change the carrying direction, the turntable is required to have an outer diameter sufficient to support the entire skid legs B6 which extend in the carrying direction, that is, an outer diameter corresponding to the overall length of the skid legs B6, and consequently, there are much restrictions to layout designing of the carrying line.